SIG M17 vs M18: The Three-Second Answer to the Military’s Two-Brother Pistols

Short answer: Mechanically, only three parts separate the SIG M17 and M18 — the slide, the barrel, and the recoil spring assembly. The M17 is the full-size version (4.7" barrel, 8.0" overall length, 29.6 oz empty), while the M18 is the compact version (3.9" barrel, 7.2" overall length, 28.1 oz empty). Both pistols share the same Fire Control Unit (FCU), the same grip height and width, and 17-round standard magazines are fully interchangeable, as are the 21-round extended magazines. The U.S. Army fields the M17 as its primary sidearm; the Marine Corps chose the M18 — and by 2026 the smaller M18 has become the more widely issued of the two. In the airsoft world, VFC offers licensed 1:1 GBB replicas of both.